Methane gas
oxygen
Oxygen was the missing thing was.
Oxygen was the important element missing in Earth's early atmosphere. It was only produced later by photosynthetic organisms.
oxygen
oxygen
nitrogen
no
photosynthsis
Hydrogen and helium
Carbon doixide
Oxygen was the element missing from Earth's early atmosphere, which eventually accumulated due to early photosynthetic organisms. This change in the atmosphere allowed for the evolution of organisms that rely on oxygen for respiration.
energy from the sun,lightening,earths heat triggered chemical reaction for the early gases of the earth combined